VAMP-2 and cellubrevin are expressed in pancreatic beta-cells and are essential for Ca(2+)-but not for GTP gamma S-induced insulin secretion.

AUTOR(ES)

Regazzi, R

RESUMO

VAMP proteins are important components of the machinery controlling docking and/or fusion of secretory vesicles with their target membrane. We investigated the expression of VAMP proteins in pancreatic beta-cells and their implication in the exocytosis of insulin. cDNA cloning revealed that VAMP-2 and cellubrevin, but not VAMP-1, are expressed in rat pancreatic islets and that their sequence is identical to that isolated from rat brain. Pancreatic beta-cells contain secretory granules that store and secrete insulin as well as synaptic-like microvesicles carrying gamma-aminobutyric acid. After subcellular fractionation on continuous sucrose gradients, VAMP-2 and cellubrevin were found to be associated with both types of secretory vesicle. The association of VAMP-2 with insulin-containing granules was confirmed by confocal microscopy of primary cultures of rat pancreatic beta-cells. Pretreatment of streptolysin-O permeabilized insulin-secreting cells with tetanus and botulinum B neurotoxins selectively cleaved VAMP-2 and cellubrevin and abolished Ca(2+)-induced insulin release (IC50 approximately 15 nM). By contrast, the pretreatment with tetanus and botulinum B neurotoxins did not prevent GTP gamma S-stimulated insulin secretion. Taken together, our results show that pancreatic beta-cells express VAMP-2 and cellubrevin and that one or both of these proteins selectively control Ca(2+)-mediated insulin secretion.

Documentos Relacionados

• Ca(2+)- and GTP-dependent exocytosis in mouse pancreatic beta-cells involves both common and distinct steps.
• Emptying of intracellular Ca2+ stores stimulates Ca2+ entry in mouse pancreatic beta-cells by both direct and indirect mechanisms.
• VAMP2, but Not VAMP3/Cellubrevin, Mediates Insulin-dependent Incorporation of GLUT4 into the Plasma Membrane of L6 Myoblasts
• Block of ATP-regulated and Ca2(+)-activated K+ channels in mouse pancreatic beta-cells by external tetraethylammonium and quinine.
• Glucose- and GTP-dependent stimulation of the carboxyl methylation of CDC42 in rodent and human pancreatic islets and pure beta cells. Evidence for an essential role of GTP-binding proteins in nutrient-induced insulin secretion.